Systems and methods for simultaneous multi-channel off-axis holography

ABSTRACT

Systems and methods for simultaneous multi-channel off-axis holography are described. Multi-channel imaging systems can include a light system including a plurality of light sources configured to generate illumination and reference beams at a plurality of wavelengths, an illumination system configured to illuminate a target object with the illumination beams, an optical assembly configured to receive a reflected target beam and condition the target beam for recording at an optical imaging system, and a reference system configured to propagate the reference beams to the optical imaging system. The reference beams are interfered with the target beam at the optical imaging system to create interference patterns, which can be recorded in a collective image having a plurality of side lobes. Holographic information in the side lobes can be combined to generate 3D images having a substantially reduced signal to noise ratio.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in part of U.S. application Ser. No.15/230,269, filed Aug. 5, 2016, entitled Systems and Methods forCoherent Three-Dimensional Optical Ranging, which claims the benefit ofU.S. Provisional Application No. 62/202,008, filed Aug. 6, 2015,entitled Coherent Three Dimensional Optical Ranging System. Thedisclosures of U.S. application Ser. No. 15/230,269 and U.S. ProvisionalApplication No. 62/202,008 are considered part of this application, andare hereby incorporated by reference in their entirety.

GOVERNMENT RIGHTS

Government Rights: This invention was made with government support underContract No. FA8650-10-D-5210/0030 awarded by the Air Force ResearchLaboratory. The government has certain rights in the invention.

TECHNICAL FIELD

This application generally relates to off-axis holography and, morespecifically, to simultaneous multi-channel off-axis holographic systemsand methods.

BACKGROUND

A need exists in many applications for improved digital holographysystems and methods. For example, digital holography may be used toidentify and assess surface defects or other characteristics in varioustypes of equipment or other objects, as well as in other applicationssuch as manufacturing, measurement, metrology, entertainment, andarchiving. Holographic information can be more useful than twodimensional (2D) imagery that captures only intensity information, asvarious features of an imaged object may not be apparent in 2D images ofthe object.

SUMMARY

The systems, methods, and devices described herein have innovativeaspects, no single one of which is indispensable or solely responsiblefor their desirable attributes. Without limiting the scope of theclaims, the summary below describes some of the advantageous features.It will be appreciated that the embodiments described in the summarybelow represent specific embodiments of the multi-channel holographicsystems and methods described herein, and are not intended to limit thescope of the present disclosure.

In one embodiment, a method for forming a collective image is described.The method comprises providing an illumination beam to an object toyield interaction light resulting from interaction between theillumination beam and the object, the illumination beam comprisingcoherent light at a plurality of wavelengths, directing at least some ofthe interaction light to an imaging sensor to form an image of theobject on the imaging sensor, and interfering at least a portion of theinteraction light with a plurality of reference beams simultaneously,thereby forming a plurality of interference patterns imaged on the imagesensor. Each reference beam has a wavelength corresponding to one of thewavelengths. The interference patterns combine with the image of theobject at the imaging sensor to form the collective image having aFourier transform that includes a plurality of side lobes in Fourierspace, each side lobe corresponding to one of the reference beams andhaving holographic information about a range of the object's spatialfrequencies.

The collective image can further include a main lobe located centrallywithin the collective image. Each side lobe can be non-overlapping withthe main lobe, the other side lobes, and complex conjugates of each sidelobe. The collective image can include at least two side lobe pairs,each side lobe pair comprising a side lobe and a complex conjugate ofthe side lobe disposed opposite the side lobe about the center of thecollective image. Each reference beam can interfere with the interactionlight and not interfere with the other reference beams. The illuminationbeam can comprise a laser beam. Each reference beam can originate from asource that also generates a portion of the illumination beam. Directingat least some of the interaction light to the imaging sensor can includeselectively blocking a portion of the interaction light at a pupil.

In another embodiment, an imaging system is described. The imagingsystem comprises a light system, an illumination system, an opticalsystem, a reference system, an optical imaging system, and an imagingsensor. The light system has a plurality of light sources, each of theplurality of light sources configured to generate an illumination beamand a reference beam comprising coherent light of the same wavelength,and each of the plurality of light sources configured to generate theillumination and reference beams at a wavelength different than thewavelength of the other of the plurality of light sources. Theillumination system is configured to receive the illumination beams fromthe light source and propagate the illumination beams from the lightsystem to a light output device to illuminate an object with theillumination beams. The optical system comprises a pupil and isconfigured to receive a target beam of light reflected from the objectand provide the target beam through the pupil to an optical imagingsystem. The reference system is configured to receive the referencebeams from the light system and propagate the reference beams to theoptical imaging system. The optical imaging system is configured toreceive the reference beams from the optical system and the target beamand to combine the reference beams with the target beam to form acollective image representing the object, the collective imagecharacterized as having a Fourier transform that includes a plurality ofside lobes in Fourier space, each side lobe corresponding to one of theplurality of reference beams and having phase information about a rangeof the object's spatial frequencies. The image sensor is configured tocapture the collective image of the object.

The optical imaging system can comprise at least one lens. The referencesystem can comprise one or more optical fibers configured to receiveeach reference beam and propagate each reference beam to the at leastone lens along a path parallel to and displaced from the target beam.The collective image can be formed at an imaging plane, and the imagesensor can be positioned at the imaging plane. The location of each sidelobe within the Fourier plane can be determined by the displacement ofthe corresponding reference beam relative to the target beam. Theimaging sensor can comprise a charge-coupled device. The imaging systemcan further comprise a non-transitory computer readable mediumconfigured to allow storage of the collective image. The imaging systemcan further comprise one or more processors in communication with thenon-transitory computer readable medium, the one or more processorsconfigured to create a 3D high-dynamic-range image based at least inpart on the phase information in the plurality of side lobes.

In another embodiment, a method of imaging is described. The methodcomprises exposing an object to a light source projecting coherent lightat a plurality of wavelengths simultaneously, obtaining a plurality ofcomplex images of the object, each of the plurality of complex imagesincluding amplitude information and phase information, at least two ofthe plurality of complex images obtained based on light detected atdifferent wavelengths, wherein the phase information of each compleximage has a corresponding dynamic range related to the wavelength of thecomplex image, and obtaining phase information from at least two compleximages of the plurality of complex images. The method further comprisesobtaining phase information corresponding to an equivalent wavelength inresponse to the phase information from the at least two complex imagesof the plurality of complex images, the phase information correspondingto the equivalent wavelength having a dynamic range that is greater thanthe dynamic ranges of the phase information of the at least two compleximages, and creating an image based at least in part on the phaseinformation corresponding to the equivalent wavelength of the pluralityof complex images.

The creating can comprise removing noise from the phase informationcorresponding to a first equivalent wavelength image associated with theplurality of complex images to produce a de-noised image, wherein thenoise is removed from the phase information corresponding to the firstequivalent wavelength image based at least in part on phase informationcorresponding to a second equivalent wavelength image associated withthe plurality of complex images, wherein the second equivalentwavelength is shorter than the first equivalent wavelength. The creatingcan comprise unwrapping the phase information corresponding to a secondequivalent wavelength image associated with the plurality of compleximages to produce an unwrapped image, wherein the phase informationcorresponding to the second equivalent wavelength image is unwrappedbased at least in part on phase information corresponding to a firstequivalent wavelength image associated with the plurality of compleximages, wherein the second equivalent wavelength is shorter than thefirst equivalent wavelength. The plurality of complex images can beobtained based on images captured simultaneously by an imaging sensor,each of the complex images comprising a side lobe in Fourier space. Eachof the side lobes can be non-overlapping with side lobes of the otherimages within the collective image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example single-channel system forrecording a collective image of a target.

FIG. 2 depicts one-dimensional and two-dimensional Fourierrepresentations of an example object and image resulting therefrom andhaving phase information.

FIG. 3 depicts an example two-dimensional image in Fourier spaceincluding a main lobe and a single side lobe pair.

FIG. 4 depicts an example process of extracting holographic data in asingle-channel off-axis spatial holographic system.

FIG. 5 schematically illustrates an example multi-channel system forrecording a collective image of a target.

FIG. 6 depicts an example configuration of the multi-channel system ofFIG. 5.

FIG. 7 depicts an example configuration of a reference system of thesystem of FIG. 6.

FIG. 8 depicts an example configuration of an illumination system of thesystem of FIG. 6.

FIG. 9 depicts an example two-dimensional image in Fourier spaceincluding a main lobe and four side lobe pairs.

FIG. 10 depicts an example process of creating a high-dynamic-rangeimage based on complex images obtained at a plurality of wavelengths.

FIG. 11 depicts an example process of creating a high-dynamic-rangeimage based on a plurality of complex images of an example object.

FIG. 12 is a flowchart depicting an example method of forming acollective image with a multi-channel system.

FIG. 13 is a flowchart depicting an example method of 3Dhigh-dynamic-range imaging.

DETAILED DESCRIPTION

Throughout the specification, multi-channel holographic systems andmethods are described with reference to high-dynamic-range 3D imagingapplications. 3D imaging applications are a specific embodiment ofmulti-channel holography, and it will be appreciated that the techniquesdescribed herein can equally be applied to other holographicapplications. For example, a multi-channel system in which channels areorthogonally polarized may be used to simultaneously obtain holographicinformation regarding unique polarizations, such that polarizationeffects of target surfaces can be studied. In addition, multiplepolarization channels may be able to reduce observed speckle effects ofexisting holographic imaging systems. Moreover, the 3D imagingtechniques described herein may be combined with known syntheticaperture imaging techniques to achieve further enhanced signal to noiseratio.

In further example implementations, the multiple illumination andreference channels described herein may be produced with differingtemporal and/or spatial coherence characteristics to produce multiplesets of holographic information for the same object with differenttemporal and/or spatial coherence information in each set. Accordingly,optical coherence tomography collection can be enhanced using themulti-channel techniques described herein.

Geometric information may exist at the scale of an optical wavelength.For example, holographic information obtained using a coherent lightsource (e.g., a 633 nm red laser) can provide depth information relativeto the wavelength of the light. For example, a geometric feature with adepth of 1 inch would be equivalent to more than 40,000 wavelengthsdeep. Measurement of geometric features in terms of small wavelengths,by comparing the phase of light reflected by the geometric feature to areference beam of the same wavelength, can thus provide high accuracy.However, in this method, the depth information is wrapped modulo 27c, orspatially, modulo one wavelength. More specifically, although the phasedifference between an imaging beam and a reference beam may be measuredaccurately, the actual depth z of a point of measurement is defined byz=λ(ϕ/2π)+nλ, where λ is the wavelength, ϕ is the measured phasedifference, and n is an unknown integer. Thus, when the depth variationin a geometric feature is significantly greater than the wavelength oflight, multiple depths (e.g., depths separated by integer multiples ofthe wavelength) would result in the same phase difference and beindistinguishable from one another. Thus, holographic information takenat shorter wavelengths can offer precise depth information, but can bedifficult or impossible to use without longer wavelength holographicinformation indicative of larger geometric surface features.

Multiple-wavelength holography can be used to provide larger scaleholographic information. Multiple-wavelength holography is typicallyachieved by illuminating and imaging a target object with differentwavelengths of light in a time-sequenced fashion. However, there existsa need for reliable multiple-wavelength holography outside of carefullycontrolled, stationary environments. In such implementations, cameramovement (e.g., due to movement of a user's hand), contamination,thermal growth, atmospheric change, or other error sources occurringbetween two or more time-sequenced single-wavelength holographic imagescan prevent the images from being combined to enhance the holographicinformation contained therein. Accordingly, a system capable ofsimultaneously obtaining holographic information at multiple wavelengthscan provide significant advantages over existing holographic systems.Certain embodiments of the present disclosure may use a plurality ofcomplex images (e.g., images containing both amplitude and phaseinformation) taken at a plurality of coherent wavelengths to generatedepth information accurate to relatively short length scales, but withless wrapping (e.g., consistent with longer length scales).

In some implementations, there can be a need to identify and assesssurface defects on many types of equipment. For example, organizationsthat operate equipment may have a maintenance objective which involvesassessing surface defects over the equipment. Certain embodiments canprovide an inspection process and/or system that utilizes an activelaser illumination system that emits one or more coherent wavelengths oflight and a camera which captures complex interferometric information,and is configured to determine three-dimensional (3D) surface structureinformation for defect analysis.

Certain embodiments of the present disclosure may employ a hardware andmeasurement approach to identify geometric features. Some embodimentsinclude a 3D high-dynamic-range optical imaging system.

A method of 3D high-dynamic-range imaging may include exposing an objectto a light source projecting light at a plurality of coherentwavelengths, obtaining a plurality of single-wavelength complex imagesof the object with each complex image comprising amplitude informationand phase information, and obtained based on light detected at differentwavelengths, building equivalent-wavelength complex images based oncombinations of the complex images and comprising phase informationcorresponding to an equivalent wavelength related to the wavelengths ofthe single-wavelength complex images, and unwrapping eachequivalent-wavelength image. The unwrapping of at least oneequivalent-wavelength complex image can be based, at least in part, onthe phase information of one or more other complex images of theplurality of complex images, to produce a plurality of unwrapped images.Unwrapping at least one equivalent-wavelength complex image of theplurality of complex images may be based, at least in part, oninformation obtained from unwrapping one or more other complex images ofthe plurality of complex images.

In some embodiments, image data is collected in a “snapshot” of a targetarea such that the image data for multiple wavelengths is acquired atone time, that is, at a single time or during a short period of time(e.g., less than a second) such that acquiring the image data for eachwavelength is performed simultaneously or nearly simultaneously with oneanother. The image data can include illuminating a structure with aplurality of wavelengths (e.g., 2, 3, 4, or more) of coherent light andcollecting reflected light. By using multiple wavelengths of light ofthe same area, accurate depth information or other holographicinformation can be obtained using certain embodiments described herein.Capturing the depth information for multiple wavelengths based on imagesobtained simultaneously may further reduce or eliminate noise and/orerrors that may occur due to laser drift, vibration, relative motionbetween the image acquisition device and the object to be imaged, orother error sources related to time multiplexing.

Before describing simultaneous multi-channel holographic systems, asingle-channel off-axis holography system will be described. FIG. 1schematically illustrates an example single-channel system 100 forrecording a composite image of a target 105. The system 100 includes alight source 110 which emits light to a reference system 120 and anillumination system 130. The illumination system 130 is configured toproduce an illumination beam 132 incident upon the target 105. Animaging system 140 receives a reflected target beam 134 from the target105 and sends an imaging beam 145 to an image recording system 150. Thereference system 120 is configured to send a reference beam 125 to theimage recording system 150.

The light source 110 can be any suitable source capable of producinglight at a desired wavelength. The light comprises a coherent beam oflight. For example, the light source 110 can be a laser sourceconfigured to output a coherent beam of light at a selected wavelength.In some aspects, the light source 110 may produce a single beam oflight, which can be split such that a first portion of the beam is sentto the reference system 120 and a second portion of the beam is sent tothe illumination system 130. Alternatively, one or more light sources110 may separately produce a first beam directed to the reference system120 and a second beam directed to the illumination system 130, with thefirst beam and the second beam in a phase relationship with one another(e.g., the first beam and the second beam are in phase with oneanother). The light can propagate from the light source to the referencesystem 120 through one or more single-mode optical fibers and the lightcan propagate from the light source to the illumination system 130through one or more single mode optical fibers. In certain embodiments,light can propagate from the light source to the reference system 120and/or illumination system 130 through free space propagation, fibers,and/or other optic or photonic structures, in addition to or instead ofsingle-mode optical fibers.

The reference system 120 is configured to direct a reference beam 125 tothe image recording system 150. The reference system 120 can include anynumber of optical elements, for example, one or more reflective,refractive, and/or diffractive optical elements. The reference system120 can include one or more single-mode optical fibers having a firstend disposed to receive coherent light produced by the light source 110and a second end disposed to output the coherent light as a referencebeam 125 directed toward the image recording system 150. The referencebeam 125 can be directed to pass through at least a portion of theimaging system 140, for example a lens or other optical element.

The illumination system 130 is configured to direct an illumination beam132 to the target 105. The illumination system 130 can include anynumber of optical elements, for example, one or more reflective,refractive, and/or diffractive optical elements. The illumination system130 can include one or more single-mode optical fibers having a firstend disposed to receive coherent light produced by the light source 110and a second end disposed to output the coherent light as anillumination beam 132 directed toward the target 105. The illuminationbeam 132 is incident upon the surface of the target 105. At least aportion of the illumination beam 132 is reflected by the surface of thetarget 105 to form a target beam 134 directed toward the imaging system140. The shape, texture, or other characteristics of the surface of thetarget 105 can cause the light from the illumination beam 132 to bescattered in various directions. At least a portion of the scatteredlight can be directed to propagate to the imaging system 140. The targetbeam 134 comprises the portion of the scattered light propagating to theimaging system 140. The target 105 can be transmissive, rather thanreflective, or can be a combination of transmissive and reflective.Where at least a portion of the target 105 is transmissive, the targetbeam 134 can be partially or entirely transmitted through the target 105rather than reflected from the target 105.

The imaging system 140 is configured to receive the target beam 134 andto produce an imaging beam 145 directed toward the image recordingsystem 150. Generally described, the imaging system 140 focuses orotherwise processes the light received in the target beam 134 to producean imaging beam 145 suitable for recording at the image recording system150. For example, the imaging system 140 can be configured to focus theimaging beam 145 at a desired imaging plane, for example, at thelocation of a light recording device of the image recording system 150.Accordingly, the imaging system 140 can include one or more reflective,refractive, and/or diffractive optical elements, such as one or morelenses, pupils, apertures, mirrors, filters, or the like. The imagingsystem 140 can further be configured to affect the reference beam 125.For example, the imaging system 140 may include a lens or system oflenses through which the reference beam 125 travels. Upon entering thelens or system of lenses, the target beam 134 is altered to form theimaging beam 145. The imaging system 140 can further be configured tocause the imaging beam 145 to interfere with the reference beam 125 atthe image recording system 150 so as to produce one or more interferencepatterns indicative of depth information related to the surface of thetarget 105. In certain embodiments, the system 100 can be configuredsuch that the reference beam 125 and the imaging beam 145 are combinedand imaged in an image-space plane, a pupil-space plane, or anintermediate plane.

The image recording system 150 includes a recording device such as adigital imaging sensor configured to receive and record an imageresulting from interference between the imaging beam 145 and thereference beam 125. The image resulting from the interference betweenthe imaging beam 145 and the reference beam 125 is an intensity imageincluding an interference pattern. Complex image information includingamplitude information and phase information can be decoded from theimaged interference pattern based at least in part on the knownwavelength(s) of imaged light. The imaging sensor can be acharge-coupled device (CCD), complementary metal-oxide-semiconductor(CMOS) sensor, N-type metal-oxide semiconductor (NMOS) sensor, or thelike. The image recording system 150 can include one or more memorycomponents configured to store images obtained at the imaging sensor.The imaging system 150 can further include one or more processorsconfigured to perform image processing operations such as generating oneor more 3D images based on the images obtained at the imaging sensor.

FIG. 2 depicts examples of one-dimensional and two-dimensional Fourierrepresentations of an object, and images resulting therefrom. Therepresentations shown in FIG. 2 can be obtained in an example systemsimilar to the system of FIG. 1, in which the imaging system 140includes a rectangular pupil. As will be described in greater detailbelow, the recorded image shown in the bottom row in FIG. 2 containsphase information that may be used for three-dimensional imaging.

The top row in FIG. 2 shows examples of one and two dimensional Fouriertransforms of an object. A Fourier transform of the object can bemodeled to be at the pupil plane of the system 100. Images 205 and 210are representations of the example object in 1D and 2D Fourier space(frequency domain), respectively. Image 215 is a representation of theexample object in 2D image space (spatial domain). The 2D Fourier spacerepresentation 210 in the top row is a Fourier representation of anintensity-only image obtained by the imaging sensor. Accordingly, thisimage does not contain phase information.

The middle row in FIG. 2 shows an example transfer function of thesystem 100. As shown in the respective 1D and 2D Fourier spacerepresentations 220, 225 of the transfer function, the transfer functioncorresponds to a rectangular aperture centered on the optical axis and aδ-function displaced from the optical axis. In these examples, thecentral aperture corresponds to a rectangular physical aperture, forexample, as a part of the imaging system 140. The δ-functioncorresponds, for example, to a coherent homodyne beam (e.g., a planewave arriving at an angle with respect to the imaging axis).

The bottom row in FIG. 2 shows a recorded complex image including phaseinformation. The complex image 230 in the bottom row includes a centerlobe and side lobes created by the interference of the homodyne beamwith the imaging beam. In the example shown, the side lobes are depictedas providing information, including phase information, about the exampleobject's lower spatial frequencies 232 corresponding to the centralportion 207 in example depiction 205. In some embodiments, the spatialorientation between the example object and the imaging system 140 can beadjusted so as to obtain information, including phase information, aboutthe object's higher spatial frequencies.

FIG. 3 depicts another example of a two-dimensional image 300 in Fourierspace. The two-dimensional image 300 in Fourier space includes a mainlobe 305 and a single side lobe pair, specifically side lobes 310 and310′. The image 300 can be obtained by systems and methods similar tothose described above with reference to FIGS. 1 and 2. As describedabove with reference to FIG. 2, the side lobes 310, 310′ include bothamplitude information and phase information. Side lobe 310 and side lobe310′ are complex conjugates of each other, and thus includesubstantially the same phase information. An image such as image 300generated by a single-channel system 100 generally includes a singleside-lobe pair because in this example a single homodyne beam is usedfor interference with the imaging beam. The location of the side lobes310, 310′ is dependent on the angle of the reference beam 125 relativeto the imaging beam 145 as schematically depicted in FIG. 1. Given thesystem configuration schematically depicted in FIG. 1, the two sidelobes 310, 310′ of a side lobe pair will generally disposed in oppositepositions about the center of the main lobe 305.

FIG. 4 depicts an example process of extracting holographic data in asingle-channel off-axis spatial holographic system. As shown in thedecoding process of FIG. 4, an intensity image 405 includes interferencedata due to the interference of a reference beam with an imaging beam. AFourier transform results in a Fourier-space image 410 including a pairof side lobes similar to the image 300 of FIG. 3. The side lobes can beextracted to obtain a holographic side lobe 415 which containsholographic information about the imaged object. In some embodiments,the holographic side lobe 415 can be isolated by cropping the 2D Fourierspace image 410 (e.g., by masking, chipping, stamping, or the like) toretain only the information in one of the side lobes and ignoring orexcluding the remainder of the image. Finally, the Fourier space sidelobe 415 can be transformed to a 2D image plane representation using aninverse Fourier transform. Because the side lobe 415 in Fourier spaceincluded intensity and phase information, the 2D image planerepresentation of the side lobe is a complex image including modulusinformation 420 and phase information 430.

With this understanding of a single-channel configuration, systems andmethods for simultaneous multi-channel off-axis holography will now bedescribed. FIG. 5 schematically illustrates an example of amulti-channel system 500 for recording a composite image of a target 505in accordance with certain embodiments described herein. Themulti-channel system 500 contains similar elements to the single-channelsystem 100 depicted in FIG. 1. However, the multi-channel system 500includes a plurality of light sources 510, reference systems 520, andillumination systems 530. Each light source of the plurality of lightsources 510 is configured to produce coherent light at a wavelengthdifferent from some or all of the other light sources of the pluralityof light source 510. Each light source of the plurality of light sources510 emits light to a corresponding illumination system of the pluralityof illumination systems 530 and a corresponding reference system of theplurality of reference systems 520. The multi-channel system 500 caninclude two or more channels, for example, 2, 3, 4, or more channels,depending on the number of wavelengths desired for composite imaging.For example, a 4-channel system may include 4 light sources 510, 4reference systems 520, and 4 illumination systems 530.

In various embodiments, the light sources 510 can be any suitablesources capable of producing light at desired wavelengths. In someembodiments, the light sources 510 comprise laser sources configured toproduce coherent beams of light at different wavelengths. In someaspects, each light source of the plurality of light sources 510 mayproduce a single beam of light, which can be split such that a firstportion of the beam is sent to the corresponding reference system of theplurality of reference systems 520 and a second portion of the beam issent to the corresponding illumination system of the plurality ofillumination systems 530. Alternatively, each light source 510 mayseparately produce a first beam directed to the corresponding referencesystem and a second beam directed to the corresponding illuminationsystem, with the first beam and the second beam in a phase relationshipwith one another (e.g., the first beam and the second beam are in phasewith one another). Each of the light sources 510 can comprise a singlesource configured to act as multiple sources, multiple discrete sources,or a combination thereof. In some embodiments, light propagates from thelight sources to the reference systems through one or more single-modeoptical fibers, and light propagates from the light sources to theillumination systems 530 through one or more single-mode optical fibers.In certain embodiments, light can propagate from the light sources tothe illumination systems 530 through free space propagation, fibers,and/or other optic or photonic structures, in addition to or instead ofsingle-mode optical fibers.

The reference systems 520 are configured to direct a plurality ofreference beams 525 to the image recording system 550. Each of thereference systems 520 can include one or more optical elements, forexample, one or more reflective, refractive, and/or diffractive opticalelements. In some embodiments, each of the reference systems 520includes one or more single-mode optical fibers having a first enddisposed to receive coherent light produced by the corresponding lightsource and a second end disposed to output the coherent light as one ofthe reference beams 525 directed toward the image recording system 550.In some aspects, the reference beams 525 can be directed to pass throughat least a portion of the imaging system 540, for example a lens orother optical element.

The illumination systems 530 are configured to direct a plurality ofillumination beams 532 to the target 505. Each of the illuminationsystems 530 can include one or more optical elements, for example, oneor more reflective, refractive, and/or diffractive optical elements. Insome embodiments, each of the illumination systems 530 include one ormore single-mode optical fibers having a first end disposed to receivecoherent light produced by the corresponding light source and a secondend disposed to output the coherent light as one of the illuminationbeams 532 directed toward the target 505. The illumination beams 532 areincident upon the surface of the target 505. At least a portion of theillumination beams 532 is reflected by the surface of the target 505 toform a target beam 534 directed toward the imaging system 540. It willbe appreciated that the shape, texture, or other characteristics of thesurface of the target 505 may cause the light from the illuminationbeams 532 to be scattered in various directions. At least a portion ofthe scattered light may be directed to propagate to the imaging system540. The target beam 534 comprises the portion of the scattered lightpropagating to the imaging system 540.

The imaging system 540 is configured to receive the target beam 534 andto produce an imaging beam 545 directed toward the image recordingsystem 550. Generally described, the imaging system 540 focuses orotherwise processes the light received in the target beam 534 to producean imaging beam 545 suitable for recording at the image recording system550. For example, the imaging system 540 can be configured to focus theimaging beam 545 at a desired imaging plane, for example, at thelocation of a light recording device of the image recording system 550.Accordingly, the imaging system 540 can include one or more reflective,refractive, and/or diffractive optical elements, such as one or morelenses, pupils, apertures, mirrors, filters, or the like. In someembodiments, the imaging system 540 can further be configured to affectthe reference beams 525. For example, the imaging system 540 may includea lens or system of lenses through which the reference beams 525 travel.The target beam 534 enters the lens or system of lenses and is alteredto form the imaging beam 545. The imaging system 540 can further beconfigured to cause the imaging beam 545 to interfere with the referencebeams 525 at the image recording system 550 so as to produce one or moreinterference patterns indicative of depth information related to thesurface of the target 505. In certain embodiments, the system 500 can beconfigured such that the reference beams 525 and the imaging beam 545are combined and imaged in an image-space plane, a pupil-space plane, oran intermediate plane.

The image recording system 550 includes a recording device such as oneor more digital imaging sensors, each having a plurality of sensingelements, configured to receive and record the combination (e.g.,superposition) of the imaging beam 545 and the reference beams 525. Forexample, in various embodiments the imaging sensor of the imagerecording system 550 can be a charge-coupled device (CCD), complementarymetal-oxide-semiconductor (CMOS) sensor, N-type metal-oxidesemiconductor (NMOS) sensor, or the like. The image recording system 550can include one or more memory components configured to store imagesobtained at the imaging sensor. The imaging system 550 can furtherinclude one or more processors configured to perform image processingoperations such as generating one or more 3D images based on the imagesobtained at the imaging sensor.

The multi-channel system of FIG. 5 may be constructed such that there isno coherence or interference between channels (e.g., differentwavelengths) of light at either the image recording system 550 or target505. To achieve a lack of coherence or interference between thechannels, the various light sources 510 can be configured to outputlight having different polarization (e.g., orthogonal polarization),wavelength, temporal coherence, spatial coherence, or othercharacteristic. Moreover, the multi-channel system of FIG. 5 can befurther extended to produce additional beams, such as by splitting thelight from the light sources 510 multiple times. For example, the lightfrom light sources 510 can first be split to produce reference beams 525and illumination beams 532, which can further be split by additionalbeam splitters to produce homodyne reference and illumination beams formultiple imaging systems.

FIG. 6 depicts an example embodiment of a multi-channel system 600 inaccordance with the example multi-channel system 500 of FIG. 5. Theexample multi-channel system 600 in FIG. 6 may have certain aspects thatare similar to, or the same as, the multi-channel system 500, andaspects described with reference to FIG. 6 can be applicable toembodiments of the multi-channel system 500. However, the embodimentsdepicted in FIG. 6 and described below are particular embodiments thatdo not limit the scope of embodiments described above with reference toFIG. 5. The multi-channel system 600 can include a light system 610, areference system 620, an illumination system 630, an optical imagingsystem 640, and an image recording system 650. The multi-channel system600 is configured to generate complex images of at least a portion ofthe surface 607 of a target object 605. Although the multi-channelsystem 600 is depicted and described with four channels, eachcorresponding to one wavelength of illumination and reference light, itwill be appreciated that the system may readily be implemented with moreor fewer than four channels (e.g., 2, 3, 4, 5, 6, or more channels) byincluding an appropriate number and configuration of light sources,splitters, fibers, and other associated components of the system 600.

The light system 610 includes a plurality of light sources 612 ₁, 612 ₂,612 ₃, 612 ₄ and beam splitters 616 ₁, 616 ₂, 616 ₃, 616 ₄. Each lightsource 612 ₁, 612 ₂, 612 ₃, 612 ₄ can be a laser source configured tooutput a coherent beam of light through a corresponding single-modefiber 614 ₁, 614 ₂, 614 ₃, 614 ₄. Each light source 612 ₁, 612 ₂, 612 ₃,612 ₄ produces its coherent beam at a corresponding wavelength (e.g.,light source 612 ₁ produces light at a wavelength light source 612 ₂produces light at a wavelength λ₂, etc.). Each of the single-mode fibers614 ₁, 614 ₂, 614 ₃, 614 ₄ direct the light from the corresponding oneof the light sources 612 ₁, 612 ₂, 612 ₃, 612 ₄ to the corresponding oneof the beam splitters 616 ₁, 616 ₂, 616 ₃, 616 ₄. The beam splitters 616₁, 616 ₂, 616 ₃, 616 ₄ are configured to split the incoming light intotwo portions. A reference portion of the incoming light from each of thefibers 614 ₁, 614 ₂, 614 ₃, 614 ₄ is coupled into reference system inputfibers 622 ₁, 622 ₂, 622 ₃, 622 ₄, and an illumination portion of theincoming light is coupled into illumination system input fibers 632 ₁,632 ₂, 632 ₃, 632 ₄.

The reference system 620 can comprise the reference system input fibers622 ₁, 622 ₂, 622 ₃, 622 ₄, and can comprise reference system outputfibers 624 ₁, 624 ₂, 624 ₃, 624 ₄, as schematically illustrated in FIG.6. The reference system 620 receives the reference portions of the lightfrom the light system 610 through the reference system input fibers 622₁, 622 ₂, 622 ₃, 622 ₄. The reference system 620 is configured tocondition and aim the reference portions of the light to form discreteoff-axis reference beams 625 ₁, 625 ₂, 625 ₃, 625 ₄. The referencesystem 620 is configured to direct the light from the reference systeminput fibers 622 ₁, 622 ₂, 622 ₃, 622 ₄ through the reference systemoutput fibers 624 ₁, 624 ₂, 624 ₃, 624 ₄. After traveling through thereference system output fibers 624 ₁, 624 ₂, 624 ₃, 624 ₄, the lightexits as reference beams 625 ₁, 625 ₂, 625 ₃, 625 ₄ directed toward theoptical imaging system 640 and/or the image recording system 650. Insome embodiments, the reference system input fibers 622 ₁, 622 ₂, 622 ₃,622 ₄ and the reference system output fibers 624 ₁, 624 ₂, 624 ₃, 624 ₄can comprise opposing ends of contiguous single-mode optical fibers withno intervening optical elements. In other embodiments, the referencesystem 620 can further comprise one or more additional optical elements,such as reflective, refractive, and/or diffractive optical elementsdisposed between the reference system input fibers 622 ₁, 622 ₂, 622 ₃,622 ₄ and the reference system output fibers 624 ₁, 624 ₂, 624 ₃, 624 ₄to affect the direction, intensity, collimation, or otherwise conditionthe reference beams 625 ₁, 625 ₂, 625 ₃, 625 ₄. An example referencesystem 620 compatible with certain embodiments described herein isdescribed in greater detail with reference to FIG. 7.

The illumination system 630 can comprise the illumination system inputfibers 632 ₁, 632 ₂, 632 ₃, 632 ₄, and can comprise an illuminationsystem output 634, as schematically illustrated in FIG. 6. Theillumination system 630 receives the illumination portion of the lightfrom the light system 610 through the illumination system input fibers632 ₁, 632 ₂, 632 ₃, 632 ₄. The illumination system 630 is configured tocondition and aim the illumination portions of the light as anillumination beam 638 to illuminate the surface 607 of the target object605. The illumination system 630 couples the light from the illuminationsystem input fibers 632 ₁, 632 ₂, 632 ₃, 632 ₄ into the illuminationsystem output 634. The illumination system output 634 can comprise asingle optical fiber, a bundle of single-mode fibers, or other waveguidestructure. Light for illuminating the surface 607 of the target object605 leaves the output end 636 of the illumination system output 634 asan illumination beam 638 directed toward the target object 605. Theillumination beam 638 can comprise a single beam including light ofwavelengths λ₁, λ₂, λ₃, and λ₄, or can comprise a plurality of separatebeams in close proximity to one another. For example, if theillumination system output 634 comprises a bundle of separate fibers,the illumination beam 638 can comprise several component beams, eachemitted from one of the fibers of the output 634. In some embodiments,the illumination system input fibers 632 ₁, 632 ₂, 632 ₃, 632 ₄ andcomponent fibers of the illumination system output 634 can compriseopposing ends of contiguous single-mode optical fibers with nointervening optical elements. In other embodiments, the illuminationsystem 630 can further comprise one or more additional optical elements,such as reflective, refractive, and/or diffractive optical elementsdisposed between the illumination system input fibers 632 ₁, 632 ₂, 632₃, 632 ₄ and the illumination system output 634 to affect the direction,intensity, collimation, or otherwise condition the illumination beam638. An example illumination system 630 compatible with certainembodiments described herein is described in greater detail withreference to FIG. 8.

When the illumination beam 638 reaches the surface 607 of the targetobject 605, at least a portion of the light in the illumination beam 638is reflected and/or scattered from the surface 607. At least a portionof the reflected and/or scattered light travels as a target beam 639 tothe optical imaging system 640 and the image recording system 650. Theoptical imaging system 640 comprises one or more optical elementsconfigured to focus and direct the target beam 639 to the imagerecording system 650. In the example embodiment of FIG. 6, the opticalelements of the optical imaging system 640 include a pupil 642 and alens 644. The pupil 642 comprises a physical aperture, such as a square,rectangular, or circular aperture. The pupil 642 blocks a portion of thetarget beam 630, while allowing a selected portion of the target beam630 to pass through to the lens 644 as a limited target beam 645. Thelimited target beam 645 passes through the lens 644 to become an imagingbeam 645′. The imaging beam 645′ is focused at an imaging plane, whichcoincides with an imaging sensor 652 of the image recording system 650.The reference beams 625 ₁, 625 ₂, 625 ₃, 625 ₄ also pass through thelens 644 and are directed as refracted reference beams 625 ₁′, 625 ₂′,625 ₃′, 625 ₄′. The refracted reference beams 625 ₁′, 625 ₂′, 625 ₃′,625 ₄′ are also incident on the image plane, such that the refractedreference beams 625 ₁′, 625 ₂′, 625 ₃′, 625 ₄′ interfere with theimaging beam 645′ to form spatial interference patterns on the imagingsensor 652.

The image recording system 650 can comprise the imaging sensor 652 andone or more computing devices 654, e.g., a processor 656 and a memory658 as schematically illustrated in FIG. 6. The imaging sensor 652 cancomprise a charge-coupled device (CCD), complementarymetal-oxide-semiconductor (CMOS) sensor, N-type metal-oxidesemiconductor (NMOS) sensor, or the like. The memory 658 is configuredto store images obtained at the imaging sensor 652. The processor 656 isconfigured to perform image processing operations such as generating oneor more 3D images based on the images obtained at the imaging sensor652.

FIG. 7 depicts an example reference system 620 and optical imagingsystem 640 in accordance with certain embodiments described herein. Asdescribed above with reference to FIG. 6, the reference system 620 cancomprise reference system output fibers 624 ₁, 624 ₂, 624 ₃, 624 ₄carrying corresponding reference portions of the light from the lightsystem 610. The reference system output fibers 624 ₁, 624 ₂, 624 ₃, 624₄ direct the reference portions of the light to reference beam outputstructures 626 ₁, 626 ₂, 626 ₃, 626 ₄, which can comprise rigidcomponents for securing the ends of the reference system output fibers624 ₁, 624 ₂, 624 ₃, 624 ₄ so as to accurately determine the directionof the reference beams leaving the reference system 620. In the examplereference system 620 of FIG. 7, the reference beams are emitted towardthe lens 644 of the optical imaging system 640 depicted in FIG. 6. Thereference beams are emitted parallel to and offset from an optical axis641, which passes centrally through the pupil 642 and the lens 644 ofthe optical imaging system 640. In addition, the reference beams areemitted from a reference launch plane 627 that is nominally one focallength f from the plane of the lens 644. At the reference launch plane627, each of the reference beams leaves its corresponding referencesystem output fiber 624 ₁, 624 ₂, 624 ₃, 624 ₄ as a divergent beam. Thelens focuses and collimates the reference beams such that each of thereference beams, upon exiting the lens 644, is a collimated beampropagating toward a central portion of the imaging plane 651 at anangle relative to the optical axis. The angle of each reference beamexiting the lens 644, relative to the optical axis 641, is generallydependent upon the focal length f of the lens 644 and the lateraldisplacement of the reference beam in the reference launch plane 627,relative to the optical axis 641.

FIG. 8 depicts an example illumination system 630 in accordance withcertain embodiments described herein. As described above with regard toFIG. 6, the illumination system 630 can comprise illumination systeminput fibers 632 ₁, 632 ₂, 632 ₃, 632 ₄ and an illumination systemoutput 634 carrying an illumination portion of the light from the lightsystem 610. The illumination system output 634 can comprise individualillumination system output fibers 634 ₁, 634 ₂, 634 ₃, 634 ₄, which canbe bundled together near the output end 636 so as to provide asubstantially uniform distribution of the different wavelengths λ₁, λ₂,λ₃, λ₄ over a portion (e.g., an imaged portion) of the surface 607 ofthe target object 605 irradiated by the illumination portion of thelight. As the individual wavelength components 638 ₁, 638 ₂, 638 ₃, 638₄ of the illumination beam 638 leave the output end 636, the lightpropagates over free space such that the individual wavelengthcomponents 638 ₁, 638 ₂, 638 ₃, 638 ₄ overlap to create thesubstantially uniform distribution. In some embodiments, theillumination system output fibers 634 ₁, 634 ₂, 634 ₃, 634 ₄ are bundledas close as possible to one another so as to approximate a point sourceof all of the wavelengths λ₁, λ₂, λ₃, λ₄.

FIG. 9 depicts an example two-dimensional collective image 900, or animage comprising a plurality of component images, in Fourier space inaccordance with certain embodiments described herein. The collectiveimage 900 includes a main lobe 905 and four pairs of side lobesincluding side lobes 910, 910′, side lobes 920, 920′, side lobes 930,930′, and side lobes 940, 940′. The image 900 is consistent with thefour-channel system 600 described with reference to FIGS. 6-8. Similarto the two-dimensional image 300 of FIG. 3, each of the side lobes 910,910′, 920, 920′, 930, 930′, 940 and 940′ comprise a complex image thatincludes both amplitude and phase information. The two side lobes ofeach side lobe pair are complex conjugates of one another and containsubstantially the same phase information (e.g., side lobes 910 and 910′form a side lobe pair 910/910′ and are complex conjugates of eachother). Similarly, side lobes 920 and 920′, side lobes 930 and 930′, andside lobes 940 and 940′ form the other three side lobe pairs, whereinthe side lobes of each pair are complex conjugates of one another andcontain substantially the same phase information. A collective image 900generated by the four-channel system 600 can comprise four side-lobepairs formed by the interference of the four homodyne reference beams625 ₁′, 625 ₂′, 625 ₃′, 625 ₄′ with the imaging beam 645′.

The location and spacing of the side lobe pairs 910/910′, 920/920′,930/930′, 940/940′ can be dependent on the angle of each refractedreference beam 625 ₁′, 625 ₂′, 625 ₃′, 625 ₄′ relative to the imagingbeam 645′ as shown in FIG. 6. The angle of each refracted reference beam625 ₁′, 625 ₂′, 625 ₃′, 625 ₄′ relative to the imaging beam 645′ may inturn be determined by the lens 644 based on location and spacing of theparallel reference beams 625 ₁′, 625 ₂′, 625 ₃′, 625 ₄′ relative to thelimited target beam 645. Thus, the location of side lobes 910, 920, 930,and 940 spaced vertically along a side of the collective image 900 isconsistent with the spacing of the four reference beam output structures626 ₁, 626 ₂, 626 ₃, 626 ₄ relative to the optical axis 641 as shown inFIG. 7. Accordingly, the Fourier space collective image 900 correspondsto an image captured at the imaging sensor 652 of FIG. 6. Efficientpacking of the side lobes within the collective image 900 can beachieved based on the sampling of the system 600. The sampling can bequantified as Q<4, where Q is defined by:

$\begin{matrix}{Q = \frac{f\#\lambda}{d_{p}}} & (1)\end{matrix}$where f# is the f-number of the imaging system 650, λ is the wavelength,and d_(p) is the pixel pitch of the imaging sensor 652. Accordingly, thesampling can be determined such that the side lobes 910, 920, 930, and940/do not overlap one another and side lobes 910′, 920′, 930′, 940′ donot overlap one another. In various embodiments, the side lobes in thecollective image 900 may or may not be overlapping. In embodiments withoverlapping side lobes, the sampling may have a different range ofvalues, for example, Q may be less than 4.

FIGS. 10 and 11 depict aspects of 3D imaging that may be achieved inaccordance with certain embodiments of multi-channel holographic systemsdescribed herein. With reference to FIGS. 10 and 11, an example processof creating a high-dynamic-range image based on a plurality of compleximages (e.g., the plurality of side lobes of a collective image) of anexample object will be described. As described above, each side lobe ofa collective image 900 comprises a complex image that includes phaseinformation. The phase information is indicative of the surface profileof the target object 605. However, the phase information only providesan unambiguous surface profile within the range of the wavelength of theimage. A multi-channel system 500, 600 as described herein may beimplemented with lasers emitting visible or infrared wavelengths (e.g.,in the range of 400 nm-700 nm). However, surface profile features of thetarget object 605 to be imaged may be in the range of millimeters,centimeters, or larger. In certain embodiments, phase information (andassociated depth information) for larger length scales can be extractedfrom complex images having phase information at shorter wavelengthsusing a property of two-wavelength holography. When holographic imagesare created using two different wavelengths, λ₁ and λ₂, the resultinghologram appears as if it were created with an equivalent wavelengthλ_(eq), where λ_(eq) is defined as:

$\begin{matrix}{\lambda_{eq} = {\frac{\lambda_{1} \cdot \lambda_{2}}{{\lambda_{1} - \lambda_{2}}}.}} & (2)\end{matrix}$

In this manner, holographic images including phase information of largeequivalent wavelengths (e.g., millimeters, centimeters, meters,kilometers, etc.), can be created by using two closely spacedwavelengths.

A 3D holographic image has components including 3D shape, 3D detail, andnoise, and the noise and level of detail will scale with the equivalentwavelength λ_(eq). The noise floor of a 3D holographic image can beequal to a fraction of λ_(eq) (e.g., λ_(eq)/n), where n is dependent onfactors such as (but not limited to): surface roughness, illuminationwavelength, illumination power, integration time, camera noise, etc.Thus, the dynamic range of a 3D holographic system can be increasedgeometrically with additional laser wavelengths. For example, a largeequivalent wavelength can provide information regarding the shape of theobject, and medium to fine equivalent wavelengths can provideinformation regarding the detail of surface features of the object.

With reference to FIGS. 9 and 10, the complex side lobes 910, 920, 930,940 of the collective image 900 can be extracted individually and aninverse Fourier transform operation can be applied to produce a compleximage for each of the wavelengths imaged. The phase component 1000 ₁,1000 ₂, 1000 ₃, 1000 ₄ of each complex image can then be used togenerate phase information (e.g., holographic information) correspondingto longer equivalent wavelengths. The wavelengths of the individuallaser sources 612 ₁, 612 ₂, 612 ₃, 612 ₄ can be selected such thatvarious combinations of light from two of the laser sources 612 ₁, 612₂, 612 ₃, 612 ₄ result in the desired equivalent wavelengths. Forexample, as shown in FIG. 10, the wavelengths can be selected such thatthe equivalent wavelength of λ₁ and λ₂ is a coarse scale wavelength(e.g., on the order of cm), the equivalent wavelength of λ₁ and λ₃ is amedium scale wavelength (e.g., on the order of mm), and the equivalentwavelength of λ₁ and λ₄ is a fine scale wavelength (e.g., on the orderof 0.1 mm or less). In this example, the wavelengths λ₁, λ₂, λ₃, and λ₄may be in increasing or decreasing order, such that the differencebetween λ₁ and λ₂ is the smallest (and the corresponding equivalentwavelength is the largest), while the difference between λ₃ and λ₄ isthe largest (and the corresponding equivalent wavelength is thesmallest). Accordingly, the two-wavelength combinations of thewavelengths λ₁, λ₂, λ₃, and λ₄ can yield a coarse scale phase imagecomponent 1050 a (resulting from the use of λ₁ and λ₂), a medium scalephase image component 1050 b (resulting from the use of λ₁ and λ₃), anda fine scale phase image component 1050 c (resulting from the use of λ₁and λ₄). In certain other embodiments, other combinations of twowavelengths of the plurality of wavelengths can be used.

With reference to FIG. 11, the phase image components 1050 a, 1050 b,1050 c can then be unwrapped, for example, from longest equivalentwavelength image to shortest based on an algorithm in accordance withcertain embodiments described herein, to reduce noise and producehigh-dynamic-range depth information. Each of the phase image components1050 a, 1050 b, 1050 c has noise in the phase data. The fine scale phaseimage component 1050 c may have an acceptably small amount of depthuncertainty due to noise, but is wrapped such that larger scale depthinformation may not be discernable. Conversely, the coarse scale phaseimage component 1050 a may have a large enough depth scale to discernthe overall shape of the object, but the depth uncertainty due to noisemay be unacceptably large. The algorithm can start with the coarsestwavelength image, which is nominally unwrapped. The coarse scale depthinformation of the target object surface can then be used to unwrap thenext coarsest λ_(eq) image. Thus, each image is unwrapped using knowndepth information from a larger λ_(eq) image until the finest scale isunwrapped. This algorithm can essentially force each λ_(eq) image toagree with the next finest λ_(eq) image such that the phase wrapping ofthe finest length scales is substantially mitigated.

FIG. 12 is a flowchart depicting an example method 1200 of forming acollective image using a multi-channel system in accordance with certainembodiments described herein. The method 1200 can be implemented, forexample, in a multi-channel imaging system such as systems 500 and 600described above with reference to FIGS. 5-8. The method 1200 can producea collective image comprising a main lobe and a plurality of side lobes,such as the image 900 described above with reference to FIG. 9.

The method 1200 comprises an operational block 1210, in whichillumination and reference beams are generated at each of a plurality ofwavelengths. In some embodiments, the illumination beam and thereference beam of each wavelength can be generated as a single beam oflaser energy from a laser source and split with a beam splitter. Inother embodiments, the illumination beam and the reference beam of eachwavelength can be generated by separate sources configured to generatebeams at the same wavelength. Preferably, light at different wavelengthsis generated simultaneously with one another such that the imagingmethod described herein can be performed in a simultaneous “snapshot”format using all wavelengths at the same time, rather than separatelyimaging an object in each wavelength in a time-sequenced manner.

In an operational block 1220, a target object is illuminated with theillumination beams. The illumination beams can be at least partiallycontained within one or more optical fibers, such as single mode fibers.The fibers carrying the illumination beams can be drawn close togethersuch that each of the illumination beams exits its corresponding opticalfiber in close proximity and/or adjacent to the other illuminationbeams. As the illumination beams propagate through space to the surfaceof the target object, they can spread and overlap such that a portion ofthe surface of the target object is illuminated with a substantiallyuniform distribution of each of the wavelengths of the illuminationbeams. At least a portion of each of the illumination beams incident onthe surface of the target object is reflected as interaction light. Forexample, interaction light can refer generally to some or all light froman active illumination source that has been reflected from the surfaceof an object. In some aspects, a coherent portion of an imaging beam canbe reflected by surface features of the object as interaction light withphase differences dependent on the surface feature profiles. Phasedifferences within the interaction light can then yield depthinformation about the surface features when interfered with coherentreference light of the same wavelength.

In an operational block 1230, an image of the object is formed at animaging sensor. The image can be formed based on receiving at least aportion of the interaction light at the imaging sensor. For example, aportion of the interaction light may propagate as a target beam and/oran imaging beam in the direction of the imaging sensor. Along the pathfrom the target object to the imaging sensor, the interaction light maybe conditioned, focused, or otherwise altered by one or more opticalcomponents of an optical imaging system such as the optical imagingsystems 540, 640 described above with reference to FIGS. 5 and 6.

In an operational block 1240, the interaction light is interfered withthe reference beams at the imaging sensor to create interferencepatterns. Because the interaction light and the reference beams arecoherent at the plane of the imaging sensor, each of the reference beamsinterferes with the portion of the interaction light having the samewavelength. Accordingly, an interference pattern is formed for each ofthe constituent wavelengths of the reference and illumination beams.

In an operational block 1250, the image of the object and theinterference patterns are recorded in a collective image. Theinterference patterns can be recorded as intensity information at theimaging sensor, and can be Fourier transformed to yield holographicinformation indicative of a depth or surface profile of the surface ofthe target object. The Fourier space representation of the object imagemay appear as a main lobe and the interference patterns may appear as aplurality of side lobes, as shown in FIG. 9. In some embodiments, theintensity information including interference patterns can be digitized,for example, before a Fourier transform is applied to extractholographic data. The collective image can be stored in memory incommunication with the imaging sensor. In some embodiments, thecollective image is further processed, for example, to produce one ormore 3D images. Example processing methods are described below withreference to FIG. 13.

FIG. 13 is a flowchart illustrating an example method 1300 of 3Dhigh-dynamic-range imaging in accordance with certain embodimentsdescribed herein. The method 1300 comprises an operational block 1310,in which an object is simultaneously exposed to multiple coherentwavelengths of light. The simultaneous exposure may include illuminationwith laser energy or other coherent light. For example, the object maybe illuminated by illumination beams as described above with referenceto FIGS. 5, 6, and 8. At least a portion of the light reflected by theobject is received as an imaging beam at an imaging sensor of an imagerecording system, as described with reference to FIGS. 5 and 6.

In an operational block 1320, a collective image is obtained including acomplex image corresponding to each wavelength. The collective image canbe obtained by methods such as the method described above with referenceto FIG. 12. The collective image is an image comprising a plurality ofcomponent images in image space and/or in Fourier space, some or all ofwhich may be complex images. The complex images within the collectiveimage may be side lobes in a Fourier-space collective image. Eachcomplex image includes holographic information associated withdifferences in the distances from the light source traveled by thereference and imaging beams. The collective image can be stored in amemory in communication with an imaging sensor at which the collectiveimage is captured.

In an operational block 1330, a high-dynamic-range 3D image is createdbased on the complex images. The high-dynamic-range image can be createdby one or more processors and/or other computer components incommunication with the memory in which the collective image is stored.Creation of the high-dynamic-range image in certain embodiments is doneaccording to the various processing steps described above with referenceto FIGS. 10 and 11, or through other processes. For example, in someembodiments, the phase information for various pairs of the recordedwavelengths are combined to produce phase information corresponding toan equivalent wavelength significantly longer than the two wavelengthsused to produce the equivalent wavelength phase information. Phaseinformation at several equivalent wavelengths may be combined to yieldhigh-dynamic-range depth information which has a length scale consistentwith the longest equivalent wavelength, while having a reduceddimensional uncertainty from noise (e.g., consistent with the shortestequivalent wavelength).

Although the foregoing systems and methods are described with referenceto high-dynamic-range 3D imaging applications, it will be appreciatedthat they can equally be applied to other imaging applications. Forexample, a multi-channel system in which channels are orthogonallypolarized may be used to produce an image having unique polarization ineach side lobe, such that polarization effects of target surfaces can bestudied. In addition, multiple polarization channels may be able toreduce observed speckle effects of existing holographic imaging systems.In addition, the 3D imaging techniques described herein may be combinedwith known synthetic aperture imaging techniques to achieve furtherenhanced signal to noise ratio.

In further example implementations, the multiple illumination andreference channels depicted in FIGS. 5 and 6 may be produced withdiffering temporal and/or spatial coherence characteristics to producemultiple side lobes of the same object with different temporal and/orspatial coherence information in each side lobe. Accordingly, opticalcoherence tomography collection can be enhanced using the multi-channeltechniques described herein.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like. Further, a “channel width” as used herein may encompass ormay also be referred to as a bandwidth in certain aspects.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules, and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The foregoing description details certain embodiments of the systems,devices, and methods disclosed herein. It will be appreciated, however,that no matter how detailed the foregoing appears in text, the devicesand methods can be practiced in many ways. As is also stated above, itshould be noted that the use of particular terminology when describingcertain features or aspects of the invention should not be taken toimply that the terminology is being re-defined herein to be restrictedto including any specific characteristics of the features or aspects ofthe technology with which that terminology is associated. The scope ofthe disclosure should therefore be construed in accordance with theappended claims and any equivalents thereof.

With respect to the use of any plural and/or singular terms herein,those having skill in the art can translate from the plural to thesingular and/or from the singular to the plural as is appropriate to thecontext and/or application. The various singular/plural permutations maybe expressly set forth herein for sake of clarity.

It is noted that the examples may be described as a process. Althoughthe operations may be described as a sequential process, many of theoperations can be performed in parallel, or concurrently, and theprocess can be repeated. In addition, the order of the operations may berearranged. A process is terminated when its operations are completed. Aprocess may correspond to a method, a function, a procedure, asubroutine, a subprogram, etc.

The previous description of the disclosed implementations is provided toenable any person skilled in the art to make or use the presentdisclosed process and system. Various modifications to theseimplementations will be readily apparent to those skilled in the art,and the generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thedisclosed process and system. Thus, the present disclosed process andsystem is not intended to be limited to the implementations shown hereinbut is to be accorded the widest scope consistent with the principlesand novel features disclosed herein.

What is claimed is:
 1. A method for forming a collective image, themethod comprising: providing an illumination beam to an object to yieldinteraction light resulting from interaction between the illuminationbeam and the object, the illumination beam comprising coherent light ata plurality of wavelengths; directing at least some of the interactionlight to an imaging sensor to form an image of the object on the imagingsensor; and interfering at least a portion of the interaction light witha plurality of reference beams simultaneously, thereby forming aplurality of interference patterns imaged on the image sensor; whereineach reference beam has a wavelength corresponding to one of thewavelengths; wherein the interference patterns combine with the image ofthe object at the imaging sensor to form the collective image having aFourier transform that includes a plurality of side lobes in Fourierspace, each side lobe corresponding to one of the reference beams andhaving holographic information about a range of the object's spatialfrequencies.
 2. The method of claim 1, wherein the Fourier transform ofthe collective image further comprises a main lobe located centrallywithin the Fourier transform of the collective image.
 3. The method ofclaim 2, wherein each side lobe is non-overlapping with the main lobe,the other side lobes, and complex conjugates of each side lobe.
 4. Themethod of claim 1, wherein the collective image comprises at least twoside lobe pairs, each side lobe pair comprising a side lobe and acomplex conjugate of the side lobe disposed opposite the side lobe aboutthe center of the collective image.
 5. The method of claim 1, whereineach reference beam interferes with at least a portion of theinteraction light and does not interfere with the other reference beams.6. The method of claim 1, wherein the illumination beam comprises alaser beam.
 7. The method of claim 1, wherein each reference beamoriginates from a source that also generates a portion of theillumination beam.
 8. The method of claim 1, wherein directing at leastsome of the interaction light to the imaging sensor comprisesselectively blocking a portion of the interaction light at a pupil. 9.An imaging system comprising: a light system having a plurality of lightsources, each of the plurality of light sources configured to generatean illumination beam and a reference beam comprising coherent light ofthe same wavelength, and each of the plurality of light sourcesconfigured to generate the illumination and reference beams at awavelength different than the wavelength of the other of the pluralityof light sources; an illumination system configured to receive theillumination beams from the light system and propagate the illuminationbeams from the light system to a light output device to illuminate anobject with the illumination beams; an optical system comprising apupil, the optical system configured to receive a target beam of lightreflected from the object and provide the target beam through the pupilto an optical imaging system; a reference system configured to receivethe reference beams from the light system and propagate the referencebeams to the optical imaging system; an optical imaging systemconfigured to receive the reference beams from the optical system andthe target beam and to combine the reference beams with the target beamto form a collective image representing the object, the collective imagecharacterized as having a Fourier transform that includes a plurality ofside lobes in Fourier space, each side lobe corresponding to one of theplurality of reference beams and having phase information about a rangeof the object's spatial frequencies; and an image sensor configured tocapture the collective image of the object.
 10. The imaging system ofclaim 9, wherein the optical imaging system comprises at least one lens.11. The imaging system of claim 10, wherein the reference systemcomprises one or more optical fibers configured to receive eachreference beam and propagate each reference beam to the at least onelens along a path parallel to and displaced from the target beam. 12.The imaging system of claim 8, wherein the collective image is formed atan imaging plane, and wherein the image sensor is positioned at theimaging plane.
 13. The imaging system of claim 11, wherein the locationof each side lobe within the imaging plane is determined by thedisplacement of the corresponding reference beam relative to the targetbeam.
 14. The imaging system of claim 9, wherein the imaging sensorcomprises a charge-coupled device.
 15. The imaging system of claim 9,further comprising a non-transitory computer readable medium configuredto allow storage of the collective image.
 16. The imaging system ofclaim 15, further comprising one or more processors in communicationwith the non-transitory computer readable medium, the one or moreprocessors configured to create a 3D high-dynamic-range image based atleast in part on the phase information in the plurality of side lobes.17. A method of imaging, the method comprising: exposing an object to alight source projecting coherent light at a plurality of wavelengthssimultaneously; obtaining a plurality of complex images of the object,each of the plurality of complex images including amplitude informationand phase information, at least two of the plurality of complex imagesobtained based on light detected at different wavelengths, wherein thephase information of each complex image has a corresponding dynamicrange related to the wavelength of the complex image; obtaining phaseinformation from at least two complex images of the plurality of compleximages; obtaining phase information corresponding to an equivalentwavelength in response to the phase information from the at least twocomplex images of the plurality of complex images, the phase informationcorresponding to the equivalent wavelength having a dynamic range thatis greater than the dynamic ranges of the phase information of the atleast two complex images; and creating an image based at least in parton the phase information corresponding to the equivalent wavelength ofthe plurality of complex images.
 18. The method of claim 17, wherein thecreating comprises removing noise from the phase informationcorresponding to a first equivalent wavelength image associated with theplurality of complex images to produce a de-noised image, wherein thenoise is removed from the phase information corresponding to the firstequivalent wavelength image based at least in part on phase informationcorresponding to a second equivalent wavelength image associated withthe plurality of complex images, wherein the second equivalentwavelength is shorter than the first equivalent wavelength.
 19. Themethod of claim 17, wherein the creating comprises unwrapping the phaseinformation corresponding to a second equivalent wavelength imageassociated with the plurality of complex images to produce an unwrappedimage, wherein the phase information corresponding to the secondequivalent wavelength image is unwrapped based at least in part on phaseinformation corresponding to a first equivalent wavelength imageassociated with the plurality of complex images, wherein the secondequivalent wavelength is shorter than the first equivalent wavelength.20. The method of claim 17, wherein the plurality of complex images areobtained based on images captured simultaneously by an imaging sensor,each of the complex images comprising a side lobe in Fourier space. 21.The method of claim 20, wherein each of the side lobes isnon-overlapping with side lobes of the other images within thecollective image.